This invention relates to an electric circuit breaker and, more particularly, relates to a circuit breaker that includes electromagnetic means for opposing the magnetic contact-separating forces developed when a high current flows through the contacts of the circuit breaker.
In the usual circuit breaker, the conductive path through the contacts of the circuit breaker constricts at the point of contact-engagement and thus contains portions of a generally loop-shaped configuration immediately adjacent the point of contact-engagement. Current flowing through each of these loop-shaped path portions produces magnetic forces tending to enlarge the loop, and these forces are in a direction tending to open, or separate, the contacts of the breaker. These magnetic contact-separating forces (referred to hereinafter as contact-popping forces) vary in magnitude directly with the square of the current flowing through the contacts; and hence during overcurrent and short-circuit current conditions, extremely high magnetic contact-popping forces can be developed. A more detailed explanation of how these magnetic contact-popping forces are developed is contained in U.S. Pat. No. 3,225,160-Barkan, assigned to the assignee of the present invention. Note particularly FIG. 3 thereof.
One way of holding the contacts closed against these magnetic contact-popping forces is to provide a heavy wipe spring that biases the contact together with a force greater than the maximum contact-popping forces. A disadvantage of this approach is that a large closing mechanism and operator must usually be relied upon for closing the circuit breaker against such a heavy wipe spring. such a mechanism and operator are expensive and are subject to the additional disadvantage that they subject the contacts to heavy impacts when closing the circuit breaker under light current and nocurrent conditions, when the high magnetic contact-popping are not present.